The invention relates generally to electromagnetic field testing. More particularly, the invention provides improved mode stirred electromagnetic field test chambers and associated methods for electromagnetic field testing in such chambers.
Mode stirred chambers are used for testing electromagnetic compatibility of electronic devices and the susceptibility of electronic devices to electromagnetic radiation found in the devices' operating environments. In such testing, it is necessary to isolate the equipment being tested from electromagnetic fields that would otherwise be present in the test environment, so that electromagnetic fields can be applied to the equipment under test (EUT) in a controlled way. The performance of the EUT can then be assessed based on the known electromagnetic fields that are applied to it.
Isolation chambers have been used to shield EUT from external electromagnetic fields. Such chambers include electrically conductive enclosures that shield EUT inside the enclosure from electromagnetic radiation present outside the enclosure. This allows known electromagnetic fields radiated inside the chamber to be applied to the EUT in a controlled way in isolation from unknown and variable electromagnetic fields present outside the test environment.
Known isolation chambers have been equipped with irregularly shaped, mechanically rotatable metal “paddle wheels” inside the chamber. As electromagnetic fields are generated and radiated inside the chamber, the paddle wheel is rotated, which alters the boundary conditions and transmission characteristics inside the chamber. The paddle wheel is thus said to “stir” the electromagnetic fields inside the test chamber, and such chambers are frequently referred to as “mode stirred” test chambers.
Such mechanically mode stirred test chambers have found wide use, both in testing electronic equipment for susceptibility to outside interference; and in measuring electromagnetic radiation radiated by the devices themselves. Known chambers are less than ideal, however, particularly for testing for electromagnetic radiation at relatively low frequencies.
Conventional mode stirred chambers need to have dimensions of the same order as the wavelengths of the electromagnetic energy applied during the test. In some cases, though, it was desirable to test equipment at low frequencies at which the wave-length is on the order of several hundred yards, or more. It is obviously not generally feasible to build a test chamber of anything near this size.
A need exists, therefore, for electromagnetic field test chambers and associated testing methods in which controlled and uniform electromagnetic fields can be applied to EUT, and particularly at relatively low frequencies. Such chambers should be of reasonable size, and should not be unduly complex, either in their construction or in their operation.